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Tests & Procedures : Lab Tests

D-Dimer

Does this test have other names?

What is this test?

This is a blood test to look for a substance called D-dimer. This test is used to rule out a blood clot or stroke.

D-dimer is a protein fragment made when you have a blood clot. Blood clots generally begin to slowly break down after they are formed, and this process releases D-dimer into the blood.

Why do I need this test?

You may need this test if your doctor suspects you have a dangerous blood clot. A blood clot that forms in a deep vein of the leg is called a deep vein thrombosis (DVT). It is a painful condition that can lead to life-threatening complications. If the clot travels to the lungs, it's called a pulmonary embolism (PE). Blood clots that travel to the brain can cause a stroke.

Symptoms of a blood clot include:

Leg swelling, or edema

Leg pain or tenderness, especially if it's in just one leg

Leg discoloration

Hard lump in one leg

You may also have a D-dimer test if you have symptoms of a PE, such as:

Sudden shortness of breath

Coughing up blood in your sputum

Rapid heart rate

Chest pain in the area of your lungs

People with blood clots often have one or more risk factors for thrombosis. These risk factors include:

Major surgery or trauma

Prolonged immobility, including prescribed bed rest or long trips by plane or car

Pregnancy or recent childbirth

Certain cancers

Staying in the hospital or living in a nursing home

Antiphospholipid syndrome

Broken leg requiring a cast

Inherited clotting disorder, such as factor V Leiden mutation

You may also need this test to help diagnose and monitor treatment for a condition called disseminated intravascular coagulation (DIC). This is an acute, potentially life-threatening problem that can result from some surgical procedures, liver disease, poisonous snakebites, sepsis, or a blood infection. It can also develop after childbirth. If you have DIC, your D-dimer level will most likely be higher than normal.

What other tests might I have along with this test?

The D-dimer test is meant as a supplementary test. Whatever the results of this test, you may need more testing, including platelet count, fibrinogen, and prothrombin time.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normally, D-dimer is not present in your blood. D-dimer is made only after a clot has formed and is in the process of breaking down. If you are having significant formation and breakdown of blood clots in your body, D-dimer in your blood may be elevated.

The normal range for D-dimer is less than 0.5 micrograms per milliliter. A negative D-dimer test means that a blood clot is highly unlikely.

A positive D-dimer test doesn't mean that you definitively have a clot. Rather, it's a sign that blood clots may be forming and breaking down in the body. More testing is usually needed.

If your D-dimer test is positive, your health care professional will order a follow-up test to look for signs of a clot. The first test will most likely be an imaging scan, such as a venous ultrasound to diagnose DVT or a CT angiography to diagnose PE. If a PE is suspected, more testing may include pulmonary angiography or a ventilation/perfusion scan.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

D-dimer levels can rise for other reasons and result in false-positives. Levels may be higher in people with systemic illnesses, including heart attack and cancer. D-dimer levels may also be higher if you have a condition in which fibrin, a clotting protein, is formed and then broken down, such as infection, trauma, surgery, or liver disease.